Existing brake actuators are provided with service and/or spring brake chambers. Each chamber is typically formed from two housing parts, a base (or aluminum adapter) and a housing cup, which when fit together form the chamber. A flexible circular diaphragm is provided across the chamber, with the peripheral edge of the diaphragm compressed between portions of the base and housing cup to form an air tight seal. When the brake is at rest (i.e., the chamber is not pressurized) a spring located inside the chamber locates the diaphragm against a first end of the chamber. When pressure is introduced into the chamber by air or hydraulic fluid, the diaphragm expands and locates the spring towards a second end of the chamber.
In the spring brake chamber, pressure acts to hold off the emergency brake spring during normal operation of a vehicle. In an emergency situation, the pressure escapes the chamber and the emergency brake spring expands to apply braking force. Similarly, in the service brake chamber, the pressure constantly changes as the vehicle operator applies and releases the brake controls, causing the diaphragm and thus the spring to move back and forth.
In conventional brake systems, a narrow gap is provided between portions of the base and housing cup through which the diaphragm is placed. An enlarged, widened, bent, wedge-shaped, or otherwise outwardly deformed peripheral edge of the diaphragm is positioned on the outside of this gap (relative to the center of the chamber) to prevent the diaphragm from being pulled through (known as diaphragm pullout) during movement of the diaphragm (see, e.g., U.S. Pat. No. 5,992,297). Conventional wisdom is that, absent an enlarged and/or outwardly deformed peripheral edge, the stresses placed on the diaphragm during operation would cause it to pull through the gap. In some conventional brake systems, an additional reinforcing member is attached to or provided at the enlarged peripheral edge of the diaphragm to further prevent it from being pulled through the gap (see, e.g., U.S. Pat. No. 6,988,442).
The surface area of the diaphragm inside the chamber provides the functionality of the brake actuator and is directly related to the strength thereof. To maximize the force and/or limit the release pressure provided by the actuator, the functional surface area of the diaphragm must be maximized. However, in many cases, the space available for a brake actuator on a vehicle's axle is extremely limited. This is further constrained when considering that brake actuators having diaphragms with enlarged and/or outwardly deformed peripheral edges require additional external structures such as flanges, clamps or clips to cover the enlarged peripheral edges. Such additional structures typically result in brake actuators which have a profile significantly larger than that of the functional portion of the diaphragm.
It is therefore desirable to provide brake actuators wherein the functional surface area of the diaphragm is maximized while the overall profile of the chamber is maintained or reduced.